The coupling of lithium metal-terminated polymers is a process known in the art. In accordance with this known process, a lithium metal-terminated polymer is treated with a compound having two or more functional groups containing two or more reactive sites capable of reacting with the carbon-lithium metal bonds of the lithium metal-terminated polymer. In many cases the multifunctional coupling agent thereby becomes a nucleus for the resulting structure. From this nucleus long chain polymeric branches radiate and such coupled polymers have specific properties that render them useful for particular applications.
Linear polymers are formed by employing coupling agents having two reactive sites. One type of coupling agent employed in forming linear polymers is a dihalo alkane such as dibromoethane. See G. B. U.S. Pat. No. 1,014,999. Another coupling agent employed in making linear polymers is phenyl benzoate as disclosed in U.S. Pat. No. 3,766,301. Radial polymers are formed by employing coupling agents having more than two reactive sites. Examples of such coupling agents include among others: SiCl.sub.4 --U.S. Pat. No. 3,244,664; Polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides--U.S. Pat. No. 3,281,383; Diesters--U.S. Pat. No. 3,594,452; Methoxy silanes--U.S. Pat. No. 3,880,954; Divinyl benzene--U.S. Pat. No. 3,985,830; and 1,3,5-benzenetricarboxylic acid trichloride--U.S. Pat. No. 4,104,332.
There are distinct property differences between linear polymers and radial polymers. Linear polymers have only two arms while radial polymers have three or more arms. Typically, linear polymers have good mechanical properties but poor flow at high molecular weights. Radial polymers have better flow properties than linear polymers of the same molecular weight. In the past, manufacturers would alter the molecular weight of the arms to change properties or would blend together radial polymers and linear polymers to achieve the necessary property effect.
A new process has been found that results in the preparation of a polymer having the desired polymer functionality (number of arms) without having to blend together two different polymers.